Shades of Gray

On-site graywater treatment systems offer an efficient solution for water conservation, if designers are willing to invest the time and effort.

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“Either you bring the water to L.A., or you bring L.A. to the water.” When John Huston’s character Noah Cross uttered that famous line in Chinatown, he was referring to the water-management conspiracy at the heart of the film. But he failed to list a third potential solution to water scarcity: recycling.

The battle over California’s Owens River that inspired the 1974 film may be long forgotten, but disputes over water continue today. The seven Colorado River basin states have been engaged in longstanding battles over water rights, as have Florida, Georgia, and Alabama. According to the Environmental Protection Agency, Americans use about 26 billion gallons of water daily; about 30 percent of which we send back outdoors, primarily for landscaping, and 13 of which building occupants consume.

With drought conditions affecting more than 60 percent of the lower 48 states this year, water management and conservation in buildings have become even more critical. Beyond water shortages due to extreme climate events, the environmental and economic benefits that water recycling and on-site wastewater treatment systems offer make them worthy topics for architects to understand.

Wastewater Basics
First, a quick primer on wastewater types: Graywater comprises wastewater from sinks, dishwashers, drinking fountains, showers, and laundry facilities. In commercial settings, cooling-tower blowdown and water used for cleaning equipment may also fall into this classification. Graywater does not include water that might have come into contact with fecal matter. It may be subdivided into dark graywater—the more-contaminated flow from kitchen sinks or dishwashers, containing grease and food particles—and light graywater, which comes from bathroom sinks, tubs, and showers.

Blackwater, the more contaminated counterpart to graywater, includes untreated water that contains—or has the risk of coming into contact with—human waste from toilets and urinals; some municipalities also categorize laundry water used for washing diapers as blackwater.

Because on-site wastewater treatment and reuse—particularly of blackwater—are still nascent concepts for building and health officials in the U.S., they typically extend a building’s permitting review process—and ultimately still may not be approved. But in geographies where water shortage is common, residential graywater reuse has existed for some time now, says Katie Spataro, research director of the Seattle-based Cascadia Green Building Council and the International Living Future Institute. “Many more states have now adopted regulations, particularly where they see the value [in reducing water consumption].” Regulations vary from state to state and county to county, with graywater systems more prevalent in western and southern states.

For architects unfamiliar with the design and permitting process for on-site wastewater treatment systems, installing a graywater system in tandem with other methods of water reduction—such as low-flow appliances and rainwater collection—is a big step toward reducing a building’s overall consumption of potable water.

Going Gray
Regardless of their size and capacity, graywater treatment systems generally comprise the same basic components: pipes for collection at the source and for transport to a filtering mechanism; a septic or storage tank where collected liquid is held for treatment or undergoes treatment; and a filtration system to remove waste and debris. Most systems also require a pump to move the filtered wastewater to its point of reuse, although many take advantage of gravity. For example, a building may send graywater to a lower grade outside for subsurface irrigation.